...where (key) is my API key, (zip) is the zip code, and (state) is a two digit code that you use to identify states.

The problem that I run into is that I cannot find a correct list of states and their corresponding two digit codes. What is particularly frustrating is that you have a list posted at the following address which seems like it provides the two digit codes for states. However the two digit codes on the list at this link do not match up to the data output by the above API URL.